UV rays are electromagnetic radiation having a wavelength of from around 200 to 400 nm or so, and are said to have some negative influences on human bodies. In the field of lenses for spectacles, there is increasing a demand for UV-absorbing lenses for protecting human eyes from UV rays.
Various methods are known for producing UV-absorbing plastic lenses for spectacles. The first method comprises incorporating a UV absorbent such as 2,2′-dihydroxy-4-methoxybenzophenone, 2,2′-dihydroxy-4-n-octoxybenzophenone or the like to a plastic lens monomer followed by polymerizing the monomer to give plastic lenses, as in Japanese Patent Laid-Open Nos. 50049/1975, 122501/1983, 171716/1990, 93422/1990 and 254119/1987.
The second method is for coloring plastic lenses, comprising dipping plastic lenses in an aqueous solution with a UV absorbent dispersed therein, under heat at 80 to 100° C., thereby to infiltrate the UV absorbent into the plastic lenses (Japanese Patent Laid-Open No. 230003/1989).
The third method comprises applying a substance capable of absorbing and/or scattering UV rays onto plastic lenses (Japanese Patent Laid-Open No. 265059/1997).
Of those methods, it is presumed that the majority of conventional commercially-available plastic lenses for spectacles capable of absorbing UV rays of up to 400 nm will be produced according to the second method.
The first method disclosed in Japanese Patent Laid-Open Nos. 1 71716/1990, 93422/1990 and 254119/1987 is for improving the lightfastness of plastic lenses. In case where lenses capable of absorbing UV rays of up to around 400 nm or so are produced according to the first method in which are used conventional UV absorbents (2,2′-dihydroxy-4-methoxybenzophenone, 2,2′-dihydroxy-4-n-octoxybenzophenone, etc.), and especially where diethylene glycol bisallylcarbonate which is one typical material for plastic lenses for spectacles is used for producing such UV-absorbing lenses, some problems are inevitable. One problem is that the plastic lenses produced are often extremely yellowish and their appearances are therefore poor; and another is that a large amount of the UV absorbent is used, therefore having some negative influences on the polymerization reaction, and the physical properties of the plastic lenses produced are often poor.
The second method for producing plastic lenses capable of absorbing UV rays of up to around 400 nm or so is also problematic in that the UV absorbent to be used therein must have a high degree of UV absorbability and have a suitable degree of solubility in water, and that the plastic lenses produced therein could not have a satisfactory degree of UV absorbability, or even if they could have it, the dipping time for them shall be prolonged. In place of using water as in the second method, another method of using an organic solvent has been proposed. However, this is still problematic in that the plastic lenses produced therein and capable of absorbing UV rays of up to around 400 nm or so are often extremely yellowish.
The third method is also not suitable for obtaining plastic lenses capable of absorbing UV rays of up to around 400 nm or so.
Due to the deficiencies of the known methods, there exist a need for obtaining plastic lenses that are not too yellow in color and yet would be capable of absorbing UV rays of up to around 400 nm.